1. Field of the Invention
This invention relates to an ophthalmologic apparatus for examining the fundus of an eye to be examined.
2. Related Background Art
As a retinal-blood-stream meter, a laser-Doppler blood-stream meter for tracking the blood vessel in the fundus of an eye to be examined, and measuring the blood-stream velocity in the tracked blood vessel has heretofore been disclosed, for example, in Japanese Patent Application Laid-open No. 7-031596. This laser Doppler, blood-stream meter is such that a laser beam for tracking is applied to an area including a blood vessel, and the reflected light thereof is amplified by an image intensifier, whereafter it is received as a blood vessel image by an image sensor, and the position of the blood-vessel is detected from this blood vessel image, and a galvanometric mirror is feedback-controlled so that the blood vessel may come to a predetermined position, thereby effecting tracking. At this time, the quantity of reflected light of the blood-vessel image differs greatly depending on the position or the like of the blood vessel in the fundus of the eye and therefore, the adjustment of gain becomes necessary.
Also, a laser beam for measuring the blood-stream velocity is applied to the tracked blood vessel in the fundus of the eye, and reflected light, Doppler-shifted by the Doppler effect, of blood corpuscles flowing in the blood vessel and the laser beam reflected from the tissue around the blood vessel or the like interfere with each other, and a beat signal corresponding to a Doppler shift frequency is received by a photomultiplier. At this time, the beat signal that is a reflection signal also differs greatly depending on the position of the blood vessel in the fundus of the eye and therefore, the adjustment of the gain is necessary. Besides this, there is also disclosed a blood-stream meter having the correcting function for adjusting the tracking position.
In the above-described retinal blood-stream meter according to the prior art, however, measurement values need be compared with one another with the lapse of time in the same region, and to measure the same region, the operation of photographing and marking the fundus of the eye during the first measurement, and performing the re-setting of the apparatus with the photograph of the fundus of the eye as reference during the next measurement is necessary. Therefore, there arises the problem that unless recording is done accurately, the measurement position will deviate delicately.